So you really want to use a *command line tool* under windows? I can not understand why anybody would like to do this but I am asked for how to do it frequently. Here is my answer:

Since perl is not yet shipped with windows the first step is to get perl on your machine. Fetch it vom Active State:
http://www.activeperl.com/

Look at the screenshots from my perl installation. They should speak for themselfes.
It *really* took a couple of minutes
Now that perl is installed - fetch the ipcalc script. For example right-click and save it...
...to the perl directory under c:\
Of course you know how to start a command line shell under windows?
Here we are:
  1. The perl installation added "c:\perl\bin" to the PATH variable.
  2. cd to c:\perl (where you saved the ipcalc.pl script)
  3. create a batch file
  4. Ready. You can start ipcalc now. You may want to use the -n command line switch.
  5. Move the script to c:\perl\bin
    move ipcalc.bat bin